JPH04298051A - Field effect transistor of high electron mobility - Google Patents

Abstract

PURPOSE:To reduce gate leakage current in this device which isolates circuit elements by a mesa type construction. CONSTITUTION:A substrate 1 is overlaid with a layer 11 having a band gap larger than that of at last a channel layer under the coat zone with the extension of a gate electrode 7 on the side face (6a) of an insular operating region 6 consisting of a lamination of a channel forming layer 3 and a carrier (electron) supply layer 5 of larger band gap.

Description

[Detailed description of the invention]

0001

FIELD OF THE INVENTION The present invention relates to high electron mobility field effect transistors HEMT.

0002

2. Description of the Related Art Conventionally, an enlarged plan view of a high electron mobility field effect transistor (HEMT) using a two-dimensional electron gas channel, particularly an integrated circuit using this as a circuit element, is shown in FIG. As shown in the cross-sectional view taken along line A-A of No. 4, for example, a channel forming layer 3 is formed on a semi-insulating III-V compound semiconductor substrate 1 as necessary.
The spacer layer 4 and the carrier (electron) supply layer 5 are sequentially formed into MO
It is epitaxially grown by the CVD method (metal-organic chemical vapor deposition method), and mesa etching is performed from the upper layer to form a plurality of mesa grooves 10 forming each operating region (only one is shown in the figure). The island-like operating regions 6 (which are connected to each other) are formed to be electrically isolated from each other.

A gate electrode 7 made of Schottky metal and forming a Schottky barrier with respect to the carrier supply layer 5 is formed on the island-like operating regions 6 separated from each other so as to cross the island-like operating regions 6. A source electrode 8 and a drain electrode 9 are deposited, for example, in an alloyed manner, on both sides of the electrode.

The gate electrode 7 has, for example, an extending portion 7a extending across the island region 6, that is, the mesa portion, and into the mesa groove 10 around the mesa, for leading out the terminal thereof.

In this HEMT, a channel, that is, a two-dimensional electron gas layer channel, is formed at the interface of the channel forming layer 3 on the carrier supply layer 5 side by applying a predetermined voltage to the gate electrode 7. Therefore, the channel forming layer 3 is composed of a compound semiconductor layer whose band gap width is smaller than that of the carrier supply layer 5.

Therefore, when the extending portion 7a of the gate electrode 7 is formed directly on the channel forming layer 3 facing the side surface 6a of the island region 6, the channel forming layer 3
A so-called parasitic Schottky junction, which has a smaller Schottky barrier than the original Schottky gate part, is formed at the contact part with the extension part 7a of the gate electrode 7 on the side surface of the gate electrode 7, and this causes a gate leakage current.

For example, in this type of HEMT, a buffer layer 2 made of AlInAs, which has a large band gap and is lattice matched to the substrate 1, and an undoped channel made of InGaAs, which has a small band gap, are formed on a semi-insulating InP substrate 1. Layer 3, and on top of this, for example, A
The structure is such that an n-type AlInAs carrier supply layer 11 with a large band gap is epitaxially grown in sequence through an undoped spacer layer 4 made of lInAs (see, for example, Japanese Patent Publication No. 6294).

[0008] When this configuration is adopted, the channel forming layer 3 not only has a relatively small bandgap width compared to the carrier supply layer 5 but also has an I
Since nGaAs has a particularly small bandgap width as a material itself, when the extending portion 7a of the gate electrode 7 is directly deposited on the side surface 6a of the island-like region 6, this channel forming layer 3 Since a parasitic Schottky junction with a particularly low Schottky barrier occurs between A problem arises.

[0009]

[Problems to be Solved by the Invention] In order to solve these problems, Japanese Patent Application No. 1-1 filed by the present applicant
No. 91874 application ``High Electron Mobility Field Effect Transistor'' was proposed. In this HEMT, a pier island is formed with approximately the same height as the island-shaped operating area, and an extension part is formed by extending back into the pier island and the original island-shaped operating area. , the extension portion is configured to float above the side surface 6a of the island-like region 6.

However, when such a method is used, a problem may arise in mechanical strength because the gate electrode is floating above the base body.

In the present invention, in the HEMT described above, the occurrence of the gate leakage current described above is effectively avoided even though the extended portion of the gate electrode is arranged along the side surface of the island-like operating region. Make things possible.

0012

[Means for Solving the Problems] As shown in FIG. 1A, which is a schematic cross-sectional view of an example thereof, and FIG. 1B, which is a schematic cross-sectional view taken along the line BB in FIG. An island-shaped operating region 6 in which at least a channel-forming layer 3 and a carrier supply layer 5 with a larger band gap than the channel-forming layer 5 are sequentially laminated on an insulating substrate 1; The gate electrode 7 has an extending gate electrode 7, and the extending portion 7a of the gate electrode 7 is in contact with the side surface 6a of the island-like region 6 via a layer 11 having a band gap larger than the band gap of the channel forming layer 3. Extend.

[0013]

[Function] According to the above-described structure of the present invention, even when the channel forming layer 3 having a particularly small band gap faces the side surface 6a of the mesa or island-like operating region 6, this and the extending portion 7a of the gate electrode 7 Since a layer 11 with a large band gap is present between the two layers, a junction with a sufficiently high Schottky barrier is formed between this layer 11 and the gate electrode 7, that is, its extension 7a. If the band gap of the layer 11 with a large band gap is selected to be equal to or greater than the band gap in the carrier supply layer 5, leakage of gate current to the channel forming layer 3 can be controlled.

[0014]

[Example] An example of the present invention will be explained with reference to FIG.
To facilitate understanding, the field effect transistor HEMT according to the present invention will be described in detail with reference to FIG. 2 along with an example of its manufacturing method.

In this case, as shown in FIG. 2A, for example, AlI is sequentially deposited on the semi-insulating InP substrate 1 as necessary.
Buffer layer 2 made of nAs, undoped InGa
An As channel forming layer 3, a spacer layer 4 made of undoped AlInAs as needed, and an n-type Al
A carrier supply layer 5 made of InAs is sequentially epitaxially grown by MOCVD or the like.

Then, mesa etching is performed from above the channel forming layer 3 to the position indicated by the broken line in FIG. 2A using a well-known technique, and as shown in FIG. (only one is shown) forms an island-like operating region 6. Then, a layer 11 with a large bandgap made of the same material as the carrier (electron) supply layer 5 is epitaxially grown over the entire surface including the island-like operating region 6.

As shown in FIG. 2C, when this large bandgap layer 11 is n-type like the carrier supply layer 5, that is, has conductivity, there is no electrical connection between it and the other island-like region 6. Separating etching is performed to form the cutout portion 12.

Thereafter, a metal layer for forming the gate electrode 7 is formed on this layer 11 by vapor deposition or the like over the entire surface including the island-like operating region 6, and selectively etched by photography to form, for example, an island. A striped gate electrode 7 having an extension portion 7a extending across the active region 6 and above the mesa groove 10 is formed.

1A and B on both sides of this gate electrode 7.
As shown in , the source and drain electrodes 8 and 9 are formed of an alloy or the like. In this way, the HEMT according to the present invention can be constructed. In the above example, the layer 11 with a large band gap is made of the same material as the carrier supply layer 5, but the formation of the carrier supply layer 5 on the island-like operating region is omitted and the explanation is shown in FIG. 2B. The layer 11 with a large band gap,
It can also serve as the carrier supply layer 5.

Furthermore, in the example explained with reference to FIG. 2, the layer 11 with a large band gap made of the same material as the carrier supply layer 5 is formed to cover the side surface 6a of the island-like operating region 6, but at least , this layer 11 has an island-like operating region 6 in a portion where the extension portion 7a of the gate electrode 7 is formed.
It is sufficient if it is formed on the side surface 6a of the.

Further, in the above example, the layer 11 with a large band gap is formed of the same material as the carrier supply layer 5, but it can also be formed with another compound semiconductor layer with a large band gap.

Further, in the example illustrated in FIG. 2, the case is applied to a HEMT in which the carrier supply layer 5 is formed on the channel forming layer 3 via the spacer layer 4, but it is applicable to a HEMT in which the spacer layer 4 is not present. It can also be applied to

Further, as shown in FIG. 3, for example, an undoped layer of intrinsic (i-type) AlInAs, which also serves as a spacer 4, is epitaxied to a required thickness as the carrier supply layer 5, and the epitaxy is stopped. n on its surface
A source gas of SiH6, for example, Si, is supplied and the undoped AlInAs is doped with the impurity at a concentration such that the doping is saturated, that is, a so-called planar doping layer 5A is formed. This can also be used as a substantial carrier supply layer.

In this case, the layer 11 with a large band gap can be made of AlInAs that does not contain impurities, that is, an undoped layer, and in this case, the layer 11 is separated from other parts as explained in FIG. 2C. Deleted part 12
Etching for forming can be omitted.

Furthermore, in order to further increase the mutual conductance Gm, it is also possible to form an etched groove in the layer 11 directly below the area where the gate electrode 7 is formed.

In addition, the present invention can be applied to HEMTs having various configurations, not limited to the above-mentioned example.

[0027]

As described above, according to the present invention, although the extended portion 7a of the gate electrode 7 extends over the side surface 6a of the island-like operating region 6, it is possible to form a channel with at least a small band gap. By interposing the layer 11 with a large band gap between the two layers, it is possible to reliably avoid problems such as the formation of a Schottky junction with a small barrier height and an increase in gate leakage current. I can do it.

[Brief explanation of drawings]

FIG. 1 is a plan view and a cross-sectional view of a high electron mobility field effect transistor according to the present invention.

FIG. 2 is a manufacturing process diagram of an example of a field effect transistor according to the present invention.

FIG. 3 is a cross-sectional view of another example of a field effect transistor according to the invention.

FIG. 4 is a plan view of a conventional high electron mobility field effect transistor.

FIG. 5 is a sectional view taken along line AA in FIG. 4;

[Explanation of symbols]

1 Base 2 Buffer layer 3 Channel forming layer 4 Spacer layer 5 Carrier supply layer 6 Island-like operating area 6a Side 7 Gate electrode 7a Extension part 11. Large bandgap layer

Claims (1)

[Claims] 1. An island-shaped operating region in which at least a channel layer and a carrier supply layer having a larger band gap than the channel layer are sequentially laminated on an insulating or semi-insulating substrate; and the island-shaped operating region. a gate electrode having an extending portion extending from above to the outside thereof, and the extending portion of the gate electrode has a bandgap larger than the bandgap of the channel forming layer on a side surface of the island-like operating region. 1. A high electron mobility field effect transistor characterized in that the high electron mobility field effect transistor is configured such that the transistors are in contact with each other through a layer having a large band gap.